Progress in Energy and Combustion Science, Volume 70, January 2019,
In the last decades, energy scarcity has become an important issue globally. Renewable energy sources have gained importance due to limited fossil fuel reserves and increased concerns on climate change. In this regard, municipal wastewater is a remarkable energy source since huge amounts of wastewater are generated and treated all over the world every day. Conventional activated sludge (CAS) process, which has been in use for more than a century, is the most widely applied treatment method for municipal wastewater. In spite of its reliability and proven success, CAS process suffers from intensive energy requirement and lack of capability to capture a high amount of organic matter from wastewater. In order to recover the energy present in wastewater efficiently, it is crucial to up-concentrate the organics in wastewaters. Several physicochemical and biological processes may be employed for up-concentration of organics and capturing them onto sludge. Capturing of organic matter in sludge phase allows improved energy recovery through anaerobic digestion. This study aims to present a comprehensive evaluation of the current practices applied to up-concentrate organic matter in municipal wastewater. The paper discusses the most frequently used up-concentration methods by addressing lab-scale and full-scale applications with typical operational parameters as well as providing their strengths and constraints. In addition, various up-to-date treatment configurations are introduced in order to provide a future perspective in this field.